whoami - DEF CON CON 23/DEF CON 23... · game exploits are used to cheat but they can give access...

whoami

Tamas Szakaly (sghctoma)

from Hungary, the land of Pipacs , Palinka and gulash :)

pentester/developer @

OSCE

part of team Prauditors, European champion of Global Cyberlympics 2012

whatami

“ I am not a computer nerd. I prefer to be called a hacker!”

a binary guy

love crackmes and toying with protections

whatami


a binary guy


prepare for big coming out:

whatami


a binary guy


prepare for big coming out:I’ve been in love with the Win32 API for years :)

game modding

the urge to make things better

implement your own ideas

custom content: maps, models, etc.

to create

game modding

the urge to make things better

implement your own ideas

custom content: maps, models, etc.

share with others

http://www.moddb.com/

http://www.gamemodding.net/

even get paid for them

Steam Workshop

to create

to share

nobody plays alone

data exchange between client and server

complex data structures

often obscure protocols

nobody plays alone

data exchange between client and server

complex data structures

often obscure protocols

fuzzing heaven!!!

Game Engines: A 0-day’s Tale by ReVuln

scripting in games

built-in scripting engines

custom-made or embedded language

ARMA scripts

Lua-scripted video games @Wikipedia - 153 titles

Squirrel (Valve games)

purpose: dynamic maps, AI, etc.

available to modders

could scripts be really dangerous?

downloaded from the server, or with custom maps

runs on the gamer’s machine

dangerous functionality (e.g. file I/O)

poorly implemented sandboxes

easy to exploit: no need to circumvent exploit mitigations

surely I’m not the first one …

… so, why do this talk?

game exploits are used to cheat



but they can give access to your pc




also a gateway to your home network

other computers

routers

phones (VOIP and mobile)

TV sets

smart house components

security cameras




also a gateway to your home network

other computers

routers

phones (VOIP and mobile)

TV sets

smart house components

security cameras

almost nobody seems totalk about this!!!

no sandbox in Sandbox

target: Crysis 2 and the whole CryEngine3

uses Lua as a scripting engine

no sandbox whatsoever

yes, we can even call os.execute

one of the reasons I love Win32

Win32 APIs that work with files accept UNC paths

yes, LoadLibrary and ShellExecute do too

no need to write shellcode, we can load a DLL from a remote share

or execute something from a remote share

side effect: we can capture NTLM challenge-responses

slide #23

disclaimer #1: intentionally left (almost) blank, didn’t want to fly in the face of fate.

disclaimer #2: no, I do not believe in the 23 Enigma, this slide is an attempted joke.

disclaimer #3: yes, I do realize that this intentionally-left-blank slide has more content than most of the others.

the kobold who hijacked EXEs

target: DOTA2

another Lua-scriptable game

there is a sandbox, but its leaky

we can use the standard io library

use the SMB NT hash stealing trick

steal files

deploy autorun stuff

etc…

from crash to exploit

target: Digital Combat Simulator (DCS World)

THE combat flight simulator

uses Lua for mission scripting

another leaky sandbox

reported one issue, found another one

quiz: where is the leak?

quiz – backup question #1

The title of this talk is a quote - who asked that question?

quiz – backup question #2

what is my favorite movie?

when the gamer is the bad guy

target: Armed Assault 3 (ARMA3)

military combat simulator

customizable squads (name, URL, logo, etc.)

squad info from user-supplied URL

squad info is XML.. so, XXE? nope :(

but hey, it’s an SSRF :)

spy game

target: Garry’s Mod

a sandbox game based on Source Engine

lots of Lua-related bugs

lots of mitigations:

custom implementation for dangerous functions (e.g. package.loadlib)

restricted file I/O (directory traversal was possible, now it isn't)

proper Lua sandbox

tight sandbox, what to abuse?

you should be afraid of mice

target: Logitech Gaming Software

not a game, but a gaming mouse

can create profiles for all G-series Logitech peripherals

a Lua script is attached to these profiles

can script peripheral behavior

very tight Lua sandbox

@corsix’s black magic

a beautiful Lua sandbox escape by @corsix (CoH2 exploit)

he abused handcrafted Lua bytecode

1. string.dump to get bytecode string

2. modify bytecode

3. loadstring to load modified bytecode


get memory address of variable as double

hand-craft Lua variables pointing to arbitrary memory addresses


get memory address of variable as double

hand-craft Lua variables pointing to arbitrary memory addresses

arbitrary memory read-write

getting memory addresses

this part nops out OP_FORPREP in bytecode

so „x” will be treated as LUA_TNUMBER

double LUA_TNUMBER

TString* LUA_TSTRING

8 bytes 4 bytes 4 bytes

Lua number:

Lua string:

crafting arbitrary TValues


struct UpVal { GCObject *next; lu_byte tt; lu_byte marked; /*6 bytes padding*/ TValue *v; ...

GCObject *next lua_byte ttlua_byte

markedTValue *v some union

8 bytes 1 byte 1 byte 6 bytes 8 bytes


get upval’s memory address as double



upval is a TString struct

address of the actual character array?

struct TString { GCObject *next; lu_byte tt; lu_byte marked; lu_byte reserved; /*1 byte padding*/ unsigned int hash; size_t len; char s[len];



upval is a TString struct

address of the actual character array?

add 24 to the address

GCObject *nextlua_byte

tt

lua_byte marked

lua_byte reserved

hash len s[len]

24 bytes

8 bytes 1 byte 1 byte 1 byte 1 byte 4 bytes 8 bytes len bytes


modifies bytecode

magic will point to the next call frame’s LClosure


concatenate upval’s address three times

modifies bytecode

magic will point to the next call frame’s LClosure

next tt marked reserved hash len s[len]next tt marked isC nupvalues gclist env p upvals

8 bytes 1 byte 1 byte 1 byte 1 byte 4 bytes 8 bytes 8 bytes 8 bytes 8 bytes


summary: we can create a Lua variable that allows us to access data at any memory location of our choosing.

what did @corsix do?

created a coroutine variable with coroutine.wrap

using coroutine.wrap creates a CClosure on the Lua stack

this CClosure represents a function pointer to luaB_auxwrap

replaced the CClosure’s function pointer with ll_loadlib

it is basically a LoadLibrary wrapper

called the coroutine

what did I do differently?

mine is a 64 bit exploit

memory layout (struct packing)

calling convention (can’t modify function parameters)

sizeof(double) = sizeof(void *) on 64bit

the latter makes the exploit much simpler on 64bit

calling LoadLibrary directly instead of ll_loadlib

ll_loadlib vs LoadLibrary

ANSI-only Lua: ll_loadlib is just a stub – can’t use it

call native functions directly

prototype must match CClosure’s function pointer’s:

typedef int (*lua_CFunction) (lua_State *L);

LoadLibrary is a good candidate (has one pointer parameter)

calling LoadLibrary

get LoadLibraryA’s address

replace luaB_auxwrap with LoadLibraryA

overwrite the Lua state with the DLL name

can’t modify parameters (they are passed in registers)

we have to modify the data the parameter points to

call the coroutine

difficulties

how to get the address of the Lua state struct?

coroutine.running to the rescue

seemingly random crashes

debug hooks have to be disabled

more crashes

garbage collector has to be stopped

the overwritten Lua state has to be restored

how to get LoadLibrary’s address?

getting LoadLibrary’s address

simple solution

1. get address diff of LoadLibrary and luaB_auxwrap from PE

2. read address of luaB_auxwrap at runtime

3. the rest is elementary school math

more generic solution (used in my Redis exploit)

1. get address to NT header

2. get address of Import Directory

3. search for KERNEL32.DLL

4. get LoadLibrary’s address from IAT

restrictions

only 16 bytes of the Lua state can be overwritten

so DLL path must be .le 15 (+1 null byte)

if we use LoadLibraryA instead of LoadLibraryW

while using UNC paths

we can omit the .dll extension

e.g. \\evilhaxor\a\b

so we’ve got 9 characters for an IP, a NETBIOS. or a domain name

endgame

should we listen to Joshua?

sad truth: we should be security-conscious even while leisuring

don’t download anything from the Internet (duh!)

don’t play on untrusted servers

updates!! (Steam does this right)

game devs: you should thinkthrough cool new features froma security standpoint too!

contact

name: Tamas Szakaly

mail: [email protected] [email protected]

PGP fingerprint:4E1F 5E17 7A73 2C29 229A CD0B 4F2D 6CD0 9039 2984

twitter: @sghctoma

links & credits http://www.moddb.com/

http://www.gamemodding.net/

http://revuln.com/files/ReVuln_Game_Engines_0days_tale.pdf

http://en.wikipedia.org/wiki/Category:Lua-scripted_video_games

http://www.garrysmod.com/updates/

http://www.pcgamer.com/garrys-mod-cough-virus-is-cured-but-it-could-have-been-worse/

http://www.garrysmod.com/2014/04/19/exploit-fix-released/

http://www.valvetime.net/threads/gmod-has-a-lua-exploit-causing-mass-issues.244534/

http://www.unknowncheats.me/forum/arma-2-scripting/70058-evil-scripts.html

https://community.bistudio.com/wiki/

https://gist.github.com/corsix/6575486

http://www.fontspace.com/total-fontgeek-dtf-ltd/erbosdraco-nova-nbp

http://newsaint.deviantart.com/art/shall-we-play-a-game-168941908 (image on the first slide is a modified version of this, released under CC BY-NC-SA 3.0 - http://creativecommons.org/licenses/by-nc-sa/3.0/)

whoami - DEF CON CON 23/DEF CON 23... · game exploits are used to cheat but they can give access...

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